1. Field of the Invention
The present invention relates to the field of power supplies for digital systems having integrated circuit components. Specifically, the present invention relates to power supply regulation for digital systems having complex integrated circuits having variable supply current requirements.
2. Discussion of the Related Art
The continued advances in miniaturization of in CMOS VLSI technology presents heat-dissipation problems for several reasons. In CMOS technology, as the channel length decreases due to feature size shrinkage, the equivalent channel resistance for a transistor that is turned on decreases proportionally, if other parameters are held constant. One of the advantages of CMOS technology over other technologies is in fact power dissipation. In a normal CMOS logic circuit, there is no static power dissipation when the circuit is not changing states. Synchronous logic circuits typically change states at clock edges. Thus, in a typical synchronous CMOS logic circuit, power dissipation is also roughly proportional to the operating clock frequency. As clock frequencies continue to increase, the power consumption increases concurrently. Moreover, smaller feature sizes allow increased circuit density. The large, increasingly complex circuits within a single package can consume significant amounts of power. All power consumed by the integrated circuit is dissipated as heat. This heat must be dissipated in a manner which prevents the temperature of the integrated circuit within acceptable limitations. Excessive heat will destroy the integrated circuit. Because of these sources of increased power consumption in CMOS VLSI circuits, power dissipation problems increasingly challenge the system designers. System designers can provide adequate cooling and thermally conductive heat paths away from the integrated circuit into heat sinks; however, it is nonetheless desirable to reduce unnecessary heat production.
In order to reduce the power consumption of the circuit, VLSI designers have adopted the approaches of reducing the supply voltage and selective powering up and powering down of subcircuits on the same die. Because power is current times voltage, the reduction of the supply voltage proportionately reduces power consumption. Therefore, the reduction of standard supply voltages from 5 volts to 3.3 volts has reduced power consumption by one-third. Further reductions of supply voltage to about 2.5 volts and below is anticipated. (One example of this approach is the Pentium Pro from Intel.) The other approach is to turn off the power to a selected subcircuit within an integrated circuit when it is not in use and to turn the power back on when it is in use.
The use of multiple supply voltages as in the first approach discussed above is known in the art, and was used decades ago in vacuum tube circuits. However, when using selected partial powering of the integrated circuit according to the other approach, the dynamics of supply current requirements present great challenge to system designers. For example, the supply current requirement on the Pentium Pro can shift from 300 mA to a full 12 A in only 500 nanoseconds. Moreover, the "Klamath" (Intel's yet to be introduced microprocessor) requires a 350 nanosecond response time in which to significantly increase or decrease the supply current. As the complexities of programmable circuits such as CPLDs (complex programmable logic devices) and FPGAs (field programmable gate arrays) increases, the same power and heat management issues will occur, and the same approaches are likely to be adopted by designers to cope with these problems.
Presently existing ubiquitous power supplies used in personal computers are not able to change their current outputs within 350 ns while maintaining the proper supply voltage. They cannot increase their current output from a small current to a large current in only 350 ns. In addition, they cannot reduce their current from a large current to a small current in only 350 ns.
As is apparent from the above discussion, a need exists for a power supply system capable of drastically increasing or decreasing its output current within a very small period of time while constantly maintaining the specified output voltage.